Histological Evaluation of In Vivo Dose Delivery in Respiration-gated Small Animal Radiotherapy

Area of Science:

• Radiation Oncology
• Preclinical Research
• Radiobiology

Background:

• Preclinical small-animal radiotherapy is crucial for radiobiological research.
• Respiratory motion introduces geometric uncertainty and dose blurring, reducing treatment accuracy.
• Existing methods lack precise motion management for small animals.

Purpose of the Study:

• To develop and validate an integrated respiration-gated irradiation technique for mice.
• To assess the effectiveness of this technique in reducing motion-induced targeting errors.
• To provide biological evidence for the efficacy of respiratory gating.

Main Methods:

• Real-time respiratory motion tracking using an optical displacement sensor.
• X-ray beam gating with a mechanical shutter synchronized to animal's breathing.
• Ex vivo γH2AX immunofluorescence staining and image analysis to evaluate radiation field accuracy.
• Correction for tissue shrinkage to accurately measure irradiated dimensions.

Main Results:

• Respiratory gating significantly reduced the superior-inferior histological dimension in both liver (1.75 ± 0.24 mm) and lung (1.33 ± 0.19 mm) compared to ungated irradiation.
• This reduction translated to a 1.25 mm margin reduction for the liver and 1.22 mm for the lung.
• Biological evidence confirmed reduced motion-induced dose blurring with gating.

Conclusions:

• The developed respiration-gated irradiation technique effectively minimizes motion-induced targeting errors in preclinical mouse models.
• This method significantly reduces necessary treatment margins, enhancing targeting precision.
• The technique offers improved normal tissue sparing and increased accuracy in small-animal radiotherapy research.